1. Field of the Invention
The present invention relates to fixing apparatuses of image forming apparatuses which form developed images on recording media by image forming processes, such as electrophotographic processes and electrostatic recording processes.
2. Description of the Related Art
Image forming apparatuses, such as electrophotographic copying machines, printers and facsimiles, include image forming means and heating means. The image forming means forms a developed image on a recording medium, such as an electrofacsimile sheet, an electrostatic recording sheet, a transfer sheet or printing paper, by a direct or indirect (transfer) method. The heating means fixes the developed image on the recording medium by heat and pressure.
A typical heating means which has been used in image forming apparatuses is a heating roller-type fixing apparatus, as shown in FIG. 12. Such a fixing apparatus has a pair of rollers and heaters provided inside the rollers, and fixes a toner image on a recording medium by heat and pressure when it passes through the rotating rollers.
When a toner formed by a polymerization process (hereinafter referred to as a polymeric toner) is fixed in such a fixing apparatus, the toner having high flowability transferred on a recording medium will diffuse by the shock when a recording medium passes through the rollers. The resulting image will therefore be disordered.
Control of the glossiness of the image is generally performed by changing the transfer speed of the recording medium passing through the roller or by changing the temperature of the heaters. A glossy image requires a longer fixing time. Accordingly the transfer speed should be reduced to form a highly glossy image. When the glossiness is controlled by changing the temperature of the heaters, an idling time is required until the heaters reach a temperature which is desirable for the glossiness of the next image. Accordingly, a change in glossiness requires such an idling time before fixing the next image.